T.O. 33B-1-1 5-67 Table 5-6.  Ultrasonic Inspection Methods for Bonded Structures. INSPECTION METHOD Through Transmission Pulse-echo Ringing Damping Advan- tages Applicable to structures with multiple layers, with or without honeycomb. Detects unbonds between any layer or in honeycomb. Detects small defects (larger than the diameter of receiving search unit). Applicable to honeycomb structures with thick or thin skins. Detects small unbonds (search unit diameter and smaller). Applicable to complex shapes.  Detects small near-surface unbonds (larger than diameter of search unit). Applicable to multi- layered structures with thick or thin sheets. Detects unbonds between any layers.  Detects small unbonds (larger than diameter of search unit. Limita- tions Access to both sides of part required.  Does not determine layer position of unbonds.  Alignment of search units is critical. Couplant is required. Inspection rate is slow. Inspection from both sides required.  Does not detect far-side unbonds. Applicable only to honeycomb sandwich structures, usually those with single-layer skins. Couplant is required Applicable only to near-surface unbonds. Works best on unbonds between top sheet and adhesive layer, may miss unbonds on other side of adhesive. Works best on metals. Couplant required. Applicable only to laminated (non- honeycomb) structures. Access to both sides is required.  Does not determine layer position of unbond. Couplant is required. Resonance Pitch/Catch MIA Eddy-Sonic Advan- tages Locates layer position of unbonds.  Applicable to laminate or honeycomb structures.  Applicable to complex shapes. No couplant required, potential for faster scanning.  Special displays make interpretation easier. No couplant required. Can be used on irregular or curved surfaces.  Most effective on honeycomb structures: skin-to-core disbonds and core defects. No couplant required, potential for faster scanning. Limta- tions Inspection required from both sides of honeycomb structures.  Couplant required. Reduced effectiveness for unbonds greater than 0.80 inch below inspection surface. Access to both sides of honeycomb required. Probe is directional with respect to locating boundaries of unbonds. Reduced effectiveness on purely laminated structures. Works only on metals. Reduced effectiveness for unbonds farther from inspection surface and for low conductivity metals (titanium).